L.Control.Zoomslider = (function () {

	var Knob = L.Draggable.extend({
		initialize: function (element, stepHeight, knobHeight) {
			L.Draggable.prototype.initialize.call(this, element, element);
			this._element = element;

			this._stepHeight = stepHeight;
			this._knobHeight = knobHeight;

			this.on('predrag', function () {
				this._newPos.x = 0;
				this._newPos.y = this._adjust(this._newPos.y);
			}, this);
		},

		_adjust: function (y) {
			var value = Math.round(this._toValue(y));
			value = Math.max(0, Math.min(this._maxValue, value));
			return this._toY(value);
		},

		// y = k*v + m
		_toY: function (value) {
			return this._k * value + this._m;
		},
		// v = (y - m) / k
		_toValue: function (y) {
			return (y - this._m) / this._k;
		},

		setSteps: function (steps) {
			var sliderHeight = steps * this._stepHeight;
			this._maxValue = steps - 1;

			// conversion parameters
			// the conversion is just a common linear function.
            this._k = -this._stepHeight;
            this._m = sliderHeight - (this._stepHeight + this._knobHeight) / 2;
		},

		setPosition: function (y) { 
			L.DomUtil.setPosition(this._element,
								  L.point(0, this._adjust(y)));
		},

		setValue: function (v) {
			this.setPosition(this._toY(v));
		},

		getValue: function () {
			return this._toValue(L.DomUtil.getPosition(this._element).y);
		}
	});

	var Zoomslider = L.Control.extend({
		options: {
			position: 'topleft',
			// Height of zoom-slider.png in px
			stepHeight: 8,
			// Height of the knob div in px (including border)
			knobHeight: 6,
			styleNS: 'leaflet-control-zoomslider'
		},

		onAdd: function (map) {
			this._map = map;
			this._ui = this._createUI();
			this._knob = new Knob(this._ui.knob,
								  this.options.stepHeight,
								  this.options.knobHeight);

			map .whenReady(this._initKnob,           this)
				.whenReady(this._initEvents,         this)
				.whenReady(this._updateSize,         this)
				.whenReady(this._updateKnobValue,    this)
				.whenReady(this._updateDisabled,     this);
			return this._ui.bar;
		},

		onRemove: function (map) {
			map .off('zoomlevelschange',         this._updateSize,      this)
				.off('zoomend zoomlevelschange', this._updateKnobValue, this)
				.off('zoomend zoomlevelschange', this._updateDisabled,  this);
		},

		_createUI: function () {
			var ui = {},
				ns = this.options.styleNS;

			ui.bar     = L.DomUtil.create('div', ns + ' leaflet-bar'),
			ui.zoomIn  = this._createZoomBtn('in', 'top', ui.bar),
			ui.wrap    = L.DomUtil.create('div', ns + '-wrap leaflet-bar-part', ui.bar),
			ui.zoomOut = this._createZoomBtn('out', 'bottom', ui.bar),
			ui.body    = L.DomUtil.create('div', ns + '-body', ui.wrap),
			ui.knob    = L.DomUtil.create('div', ns + '-knob');

			L.DomEvent.disableClickPropagation(ui.bar);
			L.DomEvent.disableClickPropagation(ui.knob);

			return ui;
		},
		_createZoomBtn: function (zoomDir, end, container) {
			var classDef = this.options.styleNS + '-' + zoomDir
					+ ' leaflet-bar-part'
					+ ' leaflet-bar-part-' + end,
				link = L.DomUtil.create('a', classDef, container);

			link.href = '#';
			link.title = 'Zoom ' + zoomDir;

			L.DomEvent.on(link, 'click', L.DomEvent.preventDefault);

			return link;
		},

		_initKnob: function () {
			this._knob.enable();
			this._ui.body.appendChild(this._ui.knob);
		},
		_initEvents: function (map) {
			this._map
				.on('zoomlevelschange',         this._updateSize,      this)
				.on('zoomend zoomlevelschange', this._updateKnobValue, this)
				.on('zoomend zoomlevelschange', this._updateDisabled,  this);

			L.DomEvent.on(this._ui.body,    'click', this._onSliderClick, this);
			L.DomEvent.on(this._ui.zoomIn,  'click', this._zoomIn,        this);
			L.DomEvent.on(this._ui.zoomOut, 'click', this._zoomOut,       this);

			this._knob.on('dragend', this._updateMapZoom, this);
		},

		_onSliderClick: function (e) {
			var first = (e.touches && e.touches.length === 1 ? e.touches[0] : e),
				y = L.DomEvent.getMousePosition(first).y
					- L.DomUtil.getViewportOffset(this._ui.body).y; // Cache this?

			this._knob.setPosition(y);
			this._updateMapZoom();
		},

		_zoomIn: function (e) {
			this._map.zoomIn(e.shiftKey ? 3 : 1);
		},
		_zoomOut: function (e) {
			this._map.zoomOut(e.shiftKey ? 3 : 1);
		},

		_zoomLevels: function () {
			var zoomLevels = this._map.getMaxZoom() - this._map.getMinZoom() + 1;
			return zoomLevels < Infinity ? zoomLevels : 0;
		},
		_toZoomLevel: function (value) {
			return value + this._map.getMinZoom();
		},
		_toValue: function (zoomLevel) {
			return zoomLevel - this._map.getMinZoom();
		},

		_updateSize: function () {
			var steps = this._zoomLevels();

			this._ui.body.style.height = this.options.stepHeight * steps + 'px';
			this._knob.setSteps(steps);
		},
		_updateMapZoom: function () {
			this._map.setZoom(this._toZoomLevel(this._knob.getValue()));
		},
		_updateKnobValue: function () {
			this._knob.setValue(this._toValue(this._map.getZoom()));
		},
		_updateDisabled: function () {
			var zoomLevel = this._map.getZoom(),
				className = this.options.styleNS + '-disabled';

			L.DomUtil.removeClass(this._ui.zoomIn,  className);
			L.DomUtil.removeClass(this._ui.zoomOut, className);

			if (zoomLevel === this._map.getMinZoom()) {
				L.DomUtil.addClass(this._ui.zoomOut, className);
			}
			if (zoomLevel === this._map.getMaxZoom()) {
				L.DomUtil.addClass(this._ui.zoomIn, className);
			}
		}
	});

	return Zoomslider;
})();

L.Map.mergeOptions({
	zoomControl: false,
	zoomsliderControl: true
});

L.Map.addInitHook(function () {
	if (this.options.zoomsliderControl) {
		this.zoomsliderControl = new L.Control.Zoomslider();
		this.addControl(this.zoomsliderControl);
	}
});

L.control.zoomslider = function (options) {
	return new L.Control.Zoomslider(options);
};
